1. Field of the Invention
The present invention provides an optical system, and more particularly, to an optical system for a projector.
2. Descriptions of the Related Art
Currently, more projectors are adopting a solid-state light source module in combination with a phosphor element in an optical system thereof to generate light of different colors. FIG. 1 shows that in such an optical system, a solid-state light source module 10A has a plurality of laser diodes 11A. Each of the laser diodes HA is adapted to generate a laser beam 12A respectively. The laser beams 12A are then converged by a lens 13A onto a phosphor element 20A so that the phosphor element 20A is excited to emit light beams 21A of a specific color (i.e. wavelength). However, this kind of optical system has at least the following two shortcomings.
First, the laser beams 12A that are converged by the lens 13A and the converged laser beams 12A are incident onto the phosphor element 20A, and the light intensity on phosphor element 20A could be not uniform because the laser beams 12A could be not well aligned in practical manufacture. In other words, some regions of the phosphor element 20A are irradiated by more of the laser beams 12A, while some other regions are irradiated by less of the laser beams 12A. In the regions of the phosphor element 20A that are irradiated by more of the laser beams 12A, the higher temperature may decrease the exciting efficiency of the phosphor element 20A. That is, the exciting efficiency of the phosphor on the phosphor element may degrade as the temperature increases and cannot achieve the optimal exciting efficiency.
Additionally, a light spot of the laser beams 12A incident on the phosphor element 20A is not appropriately designed in terms of the shape and area thereof. This often leads to an overlarge emission area of the phosphor element 20A. That is, the Etendue of emission light of the phosphor element 20A becomes larger than what is acceptable for the light modulator (not shown) of the projector. As a consequence, light is lost because a part of the excited light beams 21A cannot be utilized by the light modulator. It shall be appreciated that the Etendue is defined as the product of a light source area and the divergence solid angle and is used to represent the geometric properties of an optical system.
To make improvements on the aforesaid two shortcomings, the positions of the individual laser diodes 11A as well as the angles and directions of the laser beams 12A must be precisely tailored and, further, all optical components between the laser diodes 11A and the phosphor element 20A must be precisely aligned. With precise alignment, the laser beams 12A can be uniformly incident on the phosphor element 20A and form a light spot of an appropriated shape and an appropriate area on the phosphor element 20A. However, this consumes time and costs and is difficult to control in practice, which is unfavorable for the production of the projector. Therefore, cheap projectors will have phosphor elements with poor exciting efficiencies and big production tolerance, and will not be able to make optimal exciting efficiency of phosphor and efficient use of the excited light beams.
Accordingly, a need exists in the art to provide an optical system that can make an improvement on at least one of the aforesaid shortcomings.